Location: Hydrology and Remote Sensing Laboratory
Title: Temporal and spatial variation of atmospherically deposited organic contaminants at high elevation in Yosemite National Park, California, USA Authors
Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 25, 2012
Publication Date: December 11, 2012
Citation: Bradford, D.F., Stanley, K.A., Tallent-Halsell, N.G., Sparling, D.W., Nash, M.S., Knapp, R.A., Simonich, S.M., Mcconnell, L.L. 2013. Temporal and spatial variation of atmospherically deposited organic contaminants at high elevation in Yosemite National Park, California, USA. Environmental Toxicology and Chemistry. 32:517-525. Interpretive Summary: The Sierra Nevada Mountains in California contain National Parks like Yosemite and Sequoia-Kings. Scientists have observed that several species of frogs and amphibians have been disappearing over the last few decades. This project was designed to measure the concentrations of several types of air pollutants present in sediments at the bottom of ponds where these frogs live and also in frog tissues. Samples were collected over several years from sites in Yosemite National Park and were compared with results from Sequoia-Kings National Park. Results of this project show that frog ponds in Sequoia-Kings do receive more pesticide pollutants from the air due to its proximity to the San Joaquin Valley, an area of intense agricultural production. Frog ponds in Yosemite National Park received more polycyclic aromatic hydrocarbons (PAHs), compounds related to automobile exhaust, due to greater traffic in this park and because the sampling stations were closer to roads. Sediment samples appear to be a good way to measure potential risks to frog populations. The concentrations of pollutants measured in tadpole samples were very low, but concentrations in sediment of some pollutants exceeded levels that could cause toxic effects in aquatic organisms.
Technical Abstract: Atmospherically deposited organic contaminants in the Sierra Nevada Mountains of California, USA, have exceeded some thresholds of concern, yet the distributions of contaminants in the mountains are not well known and there is little knowledge of temporal variation. The present study, (1) evaluated whether the concentrations of pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) at high elevations within Yosemite National Park in the central Sierra Nevada differ from concentrations observed previously in Sequoia-Kings Canyon National Parks in the southern Sierra Nevada, and (2) evaluated annual variation in contaminant concentrations in Yosemite relative to variation during summer and among sites. We sampled shallow-water sediment and tadpoles (Pseudacris sierra) in four high-elevation sites in Yosemite twice during the summers of 2006, 2007, and 2008. Both historic- and current-use pesticides showed a striking pattern of greater concentrations in both media in Sequoia-Kings Canyon than in Yosemite. By contrast, PAH concentrations in sediment were generally greater in Yosemite than Sequoia-Kings Canyon. We suggest that pesticide concentrations tend to be greater in Sequoia-Kings Canyon because of a longer air flow path over agricultural lands for this park, and that PAHs tend to be greater in Yosemite due to greater vehicular traffic in Yosemite. A general pattern of difference between Yosemite and Sequoia-Kings Canyon was not evident for total tadpole cholinesterase activity, an indicator of exposure to organophosphorus and carbamate pesticides. We evaluated variability of chemical concentrations in Yosemite for three sources of variation: among the four sites, between the two sampling periods within each year, and among the three years. All three components contributed significantly to total variation, although the relative contributions differed between sediment and tadpoles.